We've heard a few people compare this feature to what's available in TeamSnap, so we've done some research on that platform. In order to have availability tracking in TeamSnap, the minimum package required is their Basic package, costing $59.99 USD per year; and it would appear that the more popular package is the $89.99 USD per year plan.
The standard MBSportsWeb package provides teams with virtually every same feature as TeamSnap except the instant messaging and availability tracking, but we do so at a fraction of the cost - in fact, usually teams don't explicitly pay their association for their team's portion of the site.
Given that, we think it might be appropriate to build this feature as an add-on module but paid for directly by the teams, perhaps somewhere in the $19.99 - $29.99 CAD per year range. If it's on the higher end, then a portion of that could even go back to the association to help offset the regular cost of the site.
Practically speaking, it would be better for teams to NOT transfer their schedule data from the main association site to somewhere else - it's just another opportunity for a mistake to happen and extra work. So in theory the associations would promote our availability tracking in favour of an external system.